Attempts have been made to create internal combustion engines of the overhead valve, spark ignition type utilizing semi-spherical cylinder heads, and wherein the top of the reciprocating pistons are at least partially of semi-spherical form.
U.S. Pat. No. 3,154,061 is exemplary of this approach. In such engines, a fuel and air mixture is prepared externally of the engine and is compressed in the cylinder prior to being ignited by an electric spark normally from a spark plug mounted to the cylinder head.
This approach has been taken since it is known that the power output and thermal efficiency of an internal combustion engine of this type increases with the compression ratio up to a certain limit characterized by the occurrence of abnormal combustion, namely, the detonating or explosive combustion. This is produced as a result of a pressure wave associated with the combustion wave and causing ignition of the fuel carborized mixture as a consequence of the pressure increment propagated thereby and also as a result of the temperature increase attending that compression. This phenomena is undesirable as it causes considerable drop in engine output and is also may result in serious mechanical engine failure.
To resist premature detonation of the fuel-air mixture within the combustion chamber or chambers, in U.S. Pat. No. 3,451,061, and cylinder in the internal combustion engine disclosed in that patent terminates at the top by a substantially semi-spherical cylinder head in which the combustion chamber proper is formed. The combustion chamber is bound laterally by a regulated surface of a frustoconical or substantially frustoconical configuration and at the top by two faces constituting its bottom, and internally by the semi-spherical piston crowning. In such structure, the exhaust valve seat orifice and the ignition spark plug hole open in each one of the bottom faces of the chamber respectively. The face receiving the exhaust valve seat is substantially perpendicular to the center axis of the frustoconical surface and the face receiving the spark plug hole is inclined to the axis. Additionally, the plane of the inlet valve seat orifice is tangent to the lateral surface of the chamber of which the regulated structure permits the joining of the surfaces along a straight line which is both a straight line of the tangent plane and a generatrix of the chamber wall.
As a result, the flow of gaseous jets generated by the piston movement is facilitated along the cylinder head.
Further, the piston crown is shaped to accommodate the semi-spherical configuration of the cylinder head by being formed with a pair of geometrically separate oblique truncations joined along an edge line extending at right angles to the piston axis with one of the truncations opposite to the inlet valve. That truncation consists of a flat face parallel to the plane of the valve and nearly contacting the same in the piston top dead center position. The other truncation, registering with the combustion chamber proper, consists of a flat face parallel to the plane of the exhaust valve and which takes the form of a shallow recess in the region opposite the spark plug in order to provide the maximum combustion volume for the flame front when ignition is initiated. Further, the exhaust valve and the spark plug are situated in the combustion chamber in a plane at right angles to the plane formed by the axes of the two inlet and exhaust valves.
Other methods have been proposed to increase the resistance to detonation in such internal combustion engines. Some of the methods consist in providing a geometrical configuration to the combustion chamber in order to combine a progressive combustion with a strong cooling of that portion of the gaseous charge which is last burned. It has been shown that it is advantageous to use a compact combustion chamber, that is, a chamber so designed that the quotient of the surface area of its walls to the inner volume is as small as possible, and on the other hand, the advantage resulting from the positioning of the ignition plug at the hotest point so that the hot zone is not that of the last burning gaseous charge portion.
Other means for increasing the resistance to detonation are based on the effecting high turbulence of the gaseous mixture while taking advantage of the possibility of cooling any gas likely to produce an explosion.
U.S. patents representative of these approaches or methods of solving the undesired detonation or explosive combustion are U.S. Pat. Nos. 1,897,234; 2,767,695; 2,826,185; 2,843,103; 4,235,203; 4,259,933; 4,291,662; 4,300,399; and 4,324,214.
While a number of these methods are successful as indeed occurs using the teachings of U.S. Pat. No. 3,154,061, discussed in detail above, the structures are complicated, expensive, require severe modification of either or both the piston and the cylinder head, and tend to reflect adversely on attainable power and combustion efficiency.
It is, therefore, a primary object of the present invention to provide an improved internal combustions engine of the overhead cam, spark ignition type, which utilizes a semi-spherical cylinder head and piston whose top is correspondingly semi-spherical and sized to that of the cylinder head, which provides a very high compression ratio, which is devoid of knock, which maximizes engine output, and eliminates serious mechanical engine failure as a result thereof.